1. Field of the Invention
The present invention relates to the field of angioplasty, and in particular to the preparation of dilatation balloon catheters to facilitate their insertion into and through the cardiovascular system of a patient.
2. Description of the Prior Art
Percutaneous transluminal coronary angioplasty (PTCA) is a procedure which is well established for the treatment of blockages in the coronary arteries. Blockages may occur from cholesterol precipitation on the coronary wall which may be in any stage from initial deposit through aged lesions. Coronary arteries can also become blocked due to formation of thrombus.
The most widely used form of percutaneous coronary angioplasty makes use of a dilatation balloon catheter. The catheter is inserted into the patient's vascular system and guided until the balloon at the distal end of the catheter is positioned across the stenosis. A radiographic contrast fluid is then fed under pressure through an inflation lumen of the catheter to the balloon, which causes the balloon to expand outward, thereby opening the stenosis.
One important characteristic of a dilatation balloon catheter used for angioplasty is its "profile", which is determined by the outer diameter of the distal end portion of the balloon when deflated. Considerable effort has been spent in developing low profile dilatation balloon catheters by minimizing the dimensions of the core or inner tube which extends through the balloon to its distal end, and by reducing wall thickness, to the extent possible, of the balloon itself.
This outer diameter affects the ease and ability of the dilatation catheter to pass through a guide catheter, through the coronary arteries, and across a tight lesion.
In order to reduce the outer diameter of the balloon in its deflated condition, it is common to fold the balloon flat, so that two wings or flaps are formed. These two wings are then brought together in some fashion so as to reduce the overall diameter of the deflated balloon. This is commonly done by installing a sleeve or balloon protector around the deflated balloon to bring the folds together. In actual use, when inflation fluid is applied to the folded balloon, it causes the flaps to unwrap so that the balloon can inflate to its full inflated state.
While it is desirable to minimize profile, it is also desirable to provide as large as possible an inflated outer diameter of the balloon relative to the detailed profile. One practical effect is that the two flaps formed when the balloon is deflated and prepared for wrapping (during balloon protector installation) become very large relative to the core or inner tube of the catheter. The result is that it is difficult to get these two "large" flaps to fold together and squeeze out all of the "dead" space between them when folded, without damaging the catheter during balloon protector installation. The lowest deflated profile from a balloon results when the wings are folded in a manner that removes all of the interstitial space between the wings. Thus a relatively large deflated outer diameter of the balloon typically results. There is a continued need for improvements in catheter constructions and preparation techniques which achieve low profile and large inflated balloon diameters without sacrificing other characteristics.